Mass Wasting

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Mass Wasting
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Peruvian Valley Rock Avalanche, May 1970
After
Before
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Mass Wasting

• Downslope movement of stuff
• From force of gravity
• Not the same as erosion
• Follows weathering
• Mass wasting and erosion sculpt the Earths
  surface

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Controlling Factors

• Gravity
• Water saturation
• Reduces internal resistance, adds weight
• Steepness of slope
• Angle of repose
• Vegetation removal
• Plants reduce erosion, stabilize slopes
• Earthquakes
• Strong ground vibrations

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Controlling Factors

• Type of material
• Soil or bedrock
• Type of motion
• Fall - free-fall of material
• Slide - coherent material slides along defined
  surface
• Flow - material flows as viscous fluid
• Rate of movement
• Fastest Rock avalanche floats on trapped air
• Slowest Creep Inches or less per year

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Slump

• Downward sliding of material
• Moves as a whole section on a curved surface
• Usually slow and material doesnt travel far
• Often involves multiple blocks
• Usual cause is steep slopes

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Rockslide

• Blocks of bedrock break loose, slides downslope
• If unconsolidated Debris slide
• Usually where strata are inclined
• Causes
• Base of slope is undercut
• Rain or melting snow lubricates a sliding surface

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Debris Flow

• Also called mudflow
• Flow of soil containing large amounts of water
• Typically after heavy rains
• Common to semi-arid regions
• Very dangerous

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Earthflow

• Humid areas lots of moisture
• Hillsides
• Rich in clay and silt
• Slow rates Few milimeters to few meters per day

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Creep

• Slow downhill movement of material
• From repeated expansion contraction of material
• Freezing thawing/wetting drying

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Submarine Landslides

• Massive tens of km long
• Water laden sediment
• Often triggered by volcano
• Added weight of lava
• Earthquakes

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Permafrost

• Frozen ground
• Heating causes slumping
• Building structures
• Global warming

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